American politics is more competitive than ever. That’s making partisanship worse.

Then-Sen. Scott Brown (R-Mass.) pumps his fist during his reelection campaign kick-off in Worcester, Mass., in January 2012. (Charles Krupa/AP)

Frances E. Lee is a professor in the Government & Politics Department at the University of Maryland. This post is the second in our series on political polarization; an explanation of the series is here, and the inaugural post by Nolan McCarty is here.

The closeness of today’s party competition is decidedly not normal in American politics. In fact, the last three decades have seen the longest period of near parity in party competition for control of national institutions since the Civil War.

The figure below illustrates this reality. It displays a simple index of two-party competition at the national level for every Congress between 1861 and the present. The measure is just the average of the Democratic party’s share of the two-party presidential vote, House seats and Senate seats. I then display the index’s divergence from a 50-50 balance for each decade. The closer the bar to zero, the more competitive the decade. Democratic-leaning eras are shown in blue, Republican-leaning eras in red. Purple bars indicate evenly matched competition.

As is evident from this measure, the period since 1980 stands out as the longest sustained period of competitive balance between the parties since the Civil War. Our politics is distinctive for its narrow and switching national majorities. Nearly every recent election has held out the possibility of a shift in party control of one institution or another. Looking back, the period most similar to the present was the Gilded Age (1876-1896), another era of close and alternating party majorities, as well as of ferocious party conflict.

Competition fuels party conflict by raising the political stakes of every policy dispute. When control of national institutions hangs in the balance, no party wants to grant political legitimacy to its opposition by voting for the measures it champions. After all, how can a party wage an effective campaign after supporting or collaborating with its opposition on public policy? Instead, parties in a competitive environment will want to amplify the differences voters perceive between themselves and their opposition. They will continually strive to give voters an answer to the key question: “Why should you support us instead of them?” Even when the parties do not disagree in substantive terms, they still have political motivations to actively seek and find reasons to oppose one another. In an environment as closely competitive as the present, even small political advantages can be decisive in winning or losing institutional majorities.

During the long years of Democratic dominance following the New Deal, politics was less contentious in part because the national political stakes were so much lower. Democrats did not perceive themselves in danger of losing their outsized majorities. The “permanent minority” Republicans did not see a path to majority status. In such an environment, members of the minority party were more willing to bargain over legislative initiatives in which they would vote “yea” in exchange for substantive policy concessions, because such support did not grant political legitimacy to an opposition that they hoped to vanquish at the next election. Meanwhile, members of the majority party were more willing to fight about public policies internally among themselves, rather than attempting to close ranks against an opponent that had little perceived chance of winning power.

Competition for power, not only ideological polarization, contributes to our confrontational contemporary politics. As Sarah Binder and I emphasize in our contribution to the recent APSA Report on Negotiating Agreement in Politics, today’s political context disincentivizes successful bipartisan negotiation. The permanent campaign and politicians’ continual eye on the next election pervasively discourage efforts to work across party lines.

In short, the difficulties of the present moment stem from politicians’ quest for partisan advantage in an extraordinarily competitive context, as well as from their opposing political ideologies.